"The transmitter facility in Michigan uses about six acres of land and the one in Wisconsin about two acres. The operating frequency is 76 Hz."

76 Hz

A wave is disturbance that propagates through either some material medium or
space. Waves can be classified into two groups. Mechanical waves are waves that
travel though a medium. Electromagnetic waves are waves that can travel though
space. Examples of electromagnetic waves include microwaves, infrared waves, light
rays, ultraviolet waves, x-rays, gamma rays and radio waves.

Extremely Low Frequencies (ELF) transmissions are electromagnetic
waves used mainly for naval strategic communications. In general,
the frequency of ELF waves range from 3 Hz to 3000 Hz.
This particular range is important to the US Navy because of its
capability in providing a communication system for submerged submarines
during covert operations. In addition, the sea water's high electrical
conductivity prevents the detection of submarines and it's communication
with the world above which uses normal radio transmissions. The
lower the frequency of the ELF transmissions, the deeper the signal
can travel in sea water, thereby decreasing the chances of submarines
being detected by enemies. The Navvy's ELF Communications System
uses a frequency-modulation principle called minimum shift keying.
In this type of modulation, the frequency is shifted between 72 Hz
and 80 Hz with a center of 76 Hz.

Our military currently operates an ELF system with two transmitting antennas,
each located in Michigan and Wisconsin. The ELF antenna in Wisconsin is located
in Chequamegon National Forest and consists of 28 miles of antenna cable. The
ELF antenna in Michigan is located in Escanaba State Forest and consists of 56
miles of antenna cable. The antennas are able to generate ELFs as low as 10,000 feet deep below sea level and at an altitude of 80 kilometers. By targeting the
supercharged portion of the ionosphere over the Arctic, scientists are hoping
to create a virtual transmitter in space that would allow the Navy to communicate
with submarines worldwide. Many controversies have developed over the presence
of these huge transmitting antennas in Michigan and Wisconsin. Many argue that
signals are damaging the ionosphere. In 1984 Wisconsin sued the Federal government
charging that the Navy had covered up the risks of electromagnetic pollution.
Wisconsin had won the case, but the Pentagon claimed national security considerations
and got the decision thrown out.